The mechanisms that mediate cellular sensitivity to apoptotic stimuli are poorly understood. Considerable data suggests that reactive oxygen intermediates (R01s) may play a critical role in this regard. For example, the PI has demonstrated that increases in intracellular 02- appears to protect cells from Fas-mediated death. In this proposal, the PI plans to: 1) use various agents to alter intracellular 02- production in a variety of different cells types stimulated to die so that the generalizability of this observation can determined; 2) examine the effects of redox balance on caspase activity; 3) determine if Bcl-2 alters redox state in cells; 4) evaluate the effects of altered redox state on apoptosis sensitivity of tumor cells in vivo; and 5) determine if activation-associated changes in lymphocyte sensitivity to apoptotic stimuli is redox state dependent.